The project has achieved some of its objectives and milestones, including the development of new binaphthyl and carbazole based silylium ions and their behavior in chiral memory processes. We had unfortunately no time to study stable chiral anions, but were however able to carry out first catalysis tests. The preparation of optically pure or enriched organosilanes has required a lengthy sequence, such as the formation of diastereochemically distinct siloxanes, their separation and reduction into homochiral silanes. The positive point is that it also allowed us to develop a new straightforward method to prepare siloxanes from sterically hindered silanes and alcohols.
This work has been published in a high impact factor journal :
Pramanik, S.; Fernandes, A.; Liautard, V.; Pucheault, M.; Robert F., and Landais, Y.
Dehydrogenative Silylation of Alcohols Under Pd-Nanoparticle Catalysis. Chem. Eur. J. 2019, 25, 728-732.
It was also presented as a poster at the 1st Stable Carbene Symposium on carbene chemistry, Toulouse, France, November 30th 2018.
We also reported studies on the stabilization of silylium ion using internal as well as external coordination of Lewis bases. The extent of coordination has been revealed by the chirality studies. Loss of chirality at elevated temperature suggests an epimerization of the silylium ion. Thus, chirality of the silicon center in the silylium ion proved to be a useful tool to study the coordination of the silylium center with Lewis bases. Chiral memory was also clearly demonstrated at low temperature, depending on the nature of the substituents at silicon. When the silicon center was linked to a sp3 center, a certain freedom of the system allowed an efficient coordination of the highly Lewis acidic silylium center with a pyridine nitrogen and therefor a complete retention of the chirality at silicon. In contrast, when the silicon center was linked to a sp2 center, the coordination to nitrogen was weaker, then leading to a partial loss of the chiral memory. X-ray diffraction studies have been carried out recently which further support the stabilisation of the silylium cations species.
An article is under preparation and should be published during the first semester of 2019:
Pramanik, S.; Fernandes, A.; Laye, C.; Robert F., and Landais, Y.
Memory of Chirality with Silylium Ions. Manuscript under preparation, 2019.
